Radiology: CT with dose reduction detects significant renal stones

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Reducing radiation from 100 to 30 mAs resulted in similar detection of renal stones 3 mm or larger while reducing patient radiation exposure by as much as 70 percent, based on the results of a study published in the April edition of Radiology.

Following the study, Daniel H. Jin, MS and colleagues from the departments of urology and radiology at Loma Linda University School of Medicine in Loma Linda, Calif., colleagues said that multidetector CT scanning parameters should be tailored to minimize radiation exposure to the patients while helping detect clinically significant renal stones, as the researchers found that the rates of sensitivity and specificity remained similar after the reduction in tube charge.

After receiving clearance from the Department of Anatomic Pathology for their HIPAA compliant study, the researchers randomly placed three to five renal stones (with a range of 2 mm to 4 mm) in 14 human cadaveric kidneys that had no history of urinary calculi in order to determine the effect of reduced-radiation protocols on the sensitivity and specificity of the 16-dectector CT scanner in the detection of renal stones.

After placement, Jin and colleagues scanned each kidney with a 16-detector CT scanner at 100, 60 and 30 mAs while keeping other imaging parameters constant. The images were then reviewed independently by two radiologists who were blinded to the location and presence of renal calculi and the McNemar test was used to compare the sensitivity and specificity between different radiation settings for each reader, said the authors.

The researchers found that when renal stone detection rates were evaluated according to size, 3 mm–4 mm stones were detected at all tube charge settings, ranging from 86 to 90 percent for 3 mm stones, to 95 to 100 percent for 4 mm stones. However, 2 mm stones were detected at all tube charge settings 29 to 59 percent of the time.

In addition, specificity for both readers ranged from 105 to 109 of 110 without significant differences between 30 and 60 mAs to the standard 100 mAs and sensitivity ranged from 42 to 48 of 57, also without significant differences, wrote the authors.

Despite the results of the study presenting issues with smaller stone detection, Jin and colleagues noted that even a high-dose radiation protocol would not be helpful in the detection of approximately one-half of stones that are 2 mm or smaller, and that these stones typically do not require surgical intervention.

“Physicians diagnosing and treating stones should individualize the CT imaging protocols in a manner that will allow detection of clinically significant stones while at the same time reducing radiation exposures to the lowest level possible for patient safety,” concluded the authors.